Add support for variables in stack frames

[alan-knight]

Sorry for the size, this has several different things in it

• add variables in dartFramesFor (the important part)
• add a single test for that
• operate better without a connection, so we can write unit tests more easily
• provide fake implementations of WipConnection, AppInspector, and Runtime for tests
• make AppInspector extend Domain and use checkIsolate
• add a library for WebKit mirror objects not yet in wip_inspection_protocol (Property)
• add an example with more complicated scopes than the hello world example. Mostly used for manual testing so far, though I did extract hard-coded test data from it.

[grouma]

I don't follow this. Why is this required?

[alan-knight]

Domain takes an AppInspectorProvider. The AppInspectorProvider has to return the instance. When we're in the constructor for AppInspector we can't reference this, so we can't call super with an AppInspectorProvider. The only workaround I found was to give it a constructor that didn't need that.

[grouma]

Curious where this 100 value is coming from.

[alan-knight]

It's completely arbitrary. Added a TODO to make that consistent with what the VM does.

[grouma]

Can we not depend on this package for this abstraction? This will become problematic as we make use of the Chrome Debug Extension.

[alan-knight]

It needs that now because it can return RemoteObject from that package for its values. My thought was more to fold this into that package than to re-implement what it does.

Why is it problematic if we use the extension? Is the extension going to use an incompatible protocol?

[grouma]

Discussed offline. We'll likely reuse the abstractions provided by webkit_inspection_protocol but change out the actual communication layer.